Blown render

elleb86

Hi, I'm wondering if anyone has experience of this. Our house render has blown and we've been told that this is what is causing mould and water patches on our interior walls. The render looks so poor that it looks like we could easily knock it off. We currently can't afford the quotes we've had to replace the render but someone suggested we would be better knocking it off and leaving it just brick for now. We don't think it's a cavity wall. Would taking the render off help as it's just holding water in? Or would we possibly make it worse? Thanks

stuart45

A hard sand/cement render can trap moisture in the wall, especially where it's cracked and blown. However, although it might come off easily where it's blown, you might find it brings the face of the bricks off with it in other places.

elleb86

Thanks, that's a good point. I think we will just have to go for it and see what happens. 

FreeBear

elleb86 said: We currently can't afford the quotes we've had to replace the render but someone suggested we would be better knocking it off and leaving it just brick for now. We don't think it's a cavity wall. Would taking the render off help as it's just holding water in? Or would we possibly make it worse?

Assuming solid brick walls..

If the quotes you've had are for a cement based render (and that includes K-Rend) or one of these modern spray-on finishes, you need to go back and get quotes for a pure lime render. Cement renders trap moisture in the bricks, so you end up with damp problems internally, and render blowing externally (and probably taking the face of the bricks with it).

Pulling off the blown sections will allow rain to get in behind any remaining render - This will freeze in the winter months leading to further blowing and aggravating any internal damp problems. So either take the whole lot off in one go, or seal any/all cracks and leave it. Taking the lot off will leave you with an ugly brick finish. If left for any length of time, the bricks will spall and could end up being very costly to repair.

If you go back to brick and rerender, Building Regulations will kick in and require you to add insulation to the walls - This needs to be cork or woodfibre insulation with a lime finish to allow the walls to "breath". However, if you can demonstrate the work will cost more than any calculated energy saving over a (I believe) 15 year period, you are only required to do the best you can within budget.

tacpot12

We had this problem and removed the render back to brick to avoid the need to add insulation. The damp problems we were having have all gone now. It's important to realise that part of the reason that this worked is that we were also heating the room that was damp, but due to the render heat on its own couldn't drive out all the damp that was getting trapped. 

Albermarle

Assuming solid brick walls..

If the quotes you've had are for a cement based render (and that includes K-Rend) or one of these modern spray-on finishes, you need to go back and get quotes for a pure lime render. Cement renders trap moisture in the bricks, so you end up with damp problems internally, and render blowing externally (and probably taking the face of the bricks with it).

If you have a 100 year old house, with the original render ( first floor only) , solid walls and no damp issues, can it be assumed that the render is lime based? ( Just for my own future reference) . Thanks.

FreeBear

Albermarle said:

Assuming solid brick walls..

If the quotes you've had are for a cement based render (and that includes K-Rend) or one of these modern spray-on finishes, you need to go back and get quotes for a pure lime render. Cement renders trap moisture in the bricks, so you end up with damp problems internally, and render blowing externally (and probably taking the face of the bricks with it).

If you have a 100 year old house, with the original render ( first floor only) , solid walls and no damp issues, can it be assumed that the render is lime based? ( Just for my own future reference) . Thanks.

Portland cement started to gain traction during the late Victorian period, so it isn't wise to assume anything. My house, built in 1928/9 used lime mortar & plaster, but has concrete foundations & lintels. Top half had a rough cast render on the upper half - Base coat(s) being cement, and the finishing coat, lime (possibly with a bit of cement thrown in). Over the years, this top coat started to blow in places, not helped by the use of Sandtex types of masonry paints. Have stripped of this rough cast layer, patched all the cracks, and applied a skim of cement based render to give a relatively smooth finish. Figured that as the base coats are already cement, it doesn't matter what goes on top. And being just the upper half, rising damp is never going to be an issue.

Hoenir

elleb86 said:

We currently can't afford the quotes we've had to replace the render but someone suggested we would be better knocking it off and leaving it just brick for now. 

What's the age of the property. Often render was used to cover up the fact that it wasn't brickwork. Bricks being very expensive back in the day.